The thermite reduction process described in the Schmidt et al. U.S. Pat. No. 4,612,047 is useful in the production of rare earth/iron alloys from which high performance permanent magnet alloys (e.g. Nd.sub.2 Fe.sub.14 B) are in turn made. The thermite reduction process involves preparing a mixture of a rare earth fluoride, iron fluoride and calcium metal, heating this mixture under reducing conditions to a temperature sufficient to react the fluorides with the calcium metal to form a rare earth/iron alloy and a calcium fluoride slag, and then separating the alloy from the slag.
The rare earth fluoride (e.g., NdF.sub.3) used as one reactant in the thermite reduction process is typically prepared by wet or dry hydrofluorination of the corresponding trivalent rare earth oxide (e.g., Nd.sub.2 O.sub.3) The iron fluoride (e.g. FeF.sub.3) employed as another reactant (thermal booster) in the thermite reduction process is typically prepared by dry hydrofluorination of relatively expensive ferric chloride (FeCl.sub.3) or by wet hydrofluorination from a concentrated ferric chloride solution. Attempts have been made to reduce the cost of the iron fluoride reactant by dry hydrofluorination of ferric oxide (Fe.sub.2 O.sub.3) which is much less expensive than ferric chloride. Although various attempts have been made to dry hydrofluorinate Fe.sub.2 O.sub.3 at temperatures up to about 600.degree. C., none has been successful in producing iron fluoride acceptable for use in the thermite reduction process.
There nevertheless remains a continuing desire to reduce the cost of the iron fluoride reactant as a means of reducing the cost of the thermite reduction process. Moreover, any reduction in the number of individual reactants required to carry out the thermite reduction process and/or the number of processing steps required to make the rare earth fluoride and iron fluoride reactants for that process would be desirable for the same reason.
An object of the present invention is to provide a new, lower cost, wet process of making a rare earth/iron fluoride compound useful as a reactant in the thermite reduction process.
Another object of the invention is to provide a novel "solid solution" rare earth/iron fluoride compound that is useful as a reactant in the thermite reduction process in lieu of the separate rare earth fluoride reactant and iron fluoride reactant heretofore employed.